The proposed research is directed towards a further understanding of the molecular mechanisms regulating gene exppression by the bacterial virus lambda and its host Escherichia coli. One of the major goals of this work is to analyze the complex interactions among phage and bacterial proteins which regulate the choice between lytic and lysogenic growth by phage lambda; in particular, those factors which control phage repressor synthesis and lysogenization. We propose to continue our studies to determine the location of the promoter for repressor synthesis in the establishment mode and to determine the site(s) of action of the regulatory protein cII in the establishment of lysogeny. In addition we shall test our hypothesis that bacterial functions--Hf1, CAP, and cyclic AMP--and the phage regulator, cII protein, regulate activity of cII protein. We propose to develop an in vitro system by which to study control of lambda repressor synthesis. The cell-free DNA-dependent protein synthesizing system will employ new phage strains in which the easily assayed enzyme beta-galactosidase is controlled by the promoters governing transcription of the repressor gene. We will use this system to purify the phage and host proteins regulating synthesis of the lambda repressor, and determine the interactions among these proteins. We shall also continue our studies of the lambda positive regulatory protein Q, which we have shown to be an anti-terminator of transcription, by isolation and characterization of phage and bacterial mutations affecting the action of this regulatory protein. This study on phage and bacterial protein interactions will provide information concerning the specificity of macromolecular synthesis and on the control of growth.